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Subject[PATCH, v2] isdn: Fix stack corruption in isdnloop_init()

[ v2: use strlen instead of sizeof. ]

-tip testing found this stack corruption and bootup crash
in the ISDN subsystem, reported by stackprotector:

[ 25.656688] calling isdn_init+0x0/0x2c2 @ 1
[ 25.660388] ISDN subsystem Rev: 1.1.2.3/1.1.2.3/1.1.2.2/1.1.2.3/1.1.2.2/1.1.2.2
[ 25.668179] initcall isdn_init+0x0/0x2c2 returned 0 after 6510 usecs
[ 25.670005] calling isdn_bsdcomp_init+0x0/0x45 @ 1
[ 25.673336] PPP BSD Compression module registered
[ 25.676674] initcall isdn_bsdcomp_init+0x0/0x45 returned 0 after 3255 usecs
[ 25.680005] calling isdnloop_init+0x0/0x88 @ 1
[ 25.683337] isdnloop-ISDN-driver Rev 1.11.6.7
[ 25.686705] isdnloop: (loop0) virtual card added
[ 25.690004] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: c1de2d8b
[ 25.690006]
[ 25.693338] Pid: 1, comm: swapper Not tainted 2.6.31-rc8-tip-01250-geed031c-dirty #9565
[ 25.696672] Call Trace:
[ 25.700008] [<c190f517>] ? printk+0x1d/0x30
[ 25.703339] [<c190f45d>] panic+0x50/0xed
[ 25.706677] [<c1059194>] __stack_chk_fail+0x1e/0x42
[ 25.710005] [<c1de2d8b>] ? isdnloop_init+0x83/0x88
[ 25.713338] [<c1de2d8b>] isdnloop_init+0x83/0x88
[ 25.716674] [<c1001056>] _stext+0x56/0x15a
[ 25.720007] [<c1da8368>] kernel_init+0x8f/0xf1
[ 25.723338] [<c1da82d9>] ? kernel_init+0x0/0xf1
[ 25.726675] [<c1025c67>] kernel_thread_helper+0x7/0x58
[ 25.730005] Rebooting in 1 seconds..Press any key to enter the menu
The bug is that the temporary array:

char rev[10];

Is sized one byte too small to store strings based on
the 'revision' string.

This is a truly ancient bug: it has been introduced in
the v2.4.2.1 kernel, ~8.5 years ago, which extended
the length of 'revision' by 1 byte.

Instead of using a fixed size temporary array, size
it based on the 'revision' string.

Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
drivers/isdn/isdnloop/isdnloop.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/isdn/isdnloop/isdnloop.c b/drivers/isdn/isdnloop/isdnloop.c
index a335c85..0c8d8cb 100644
--- a/drivers/isdn/isdnloop/isdnloop.c
+++ b/drivers/isdn/isdnloop/isdnloop.c
@@ -1494,7 +1494,7 @@ static int __init
isdnloop_init(void)
{
char *p;
- char rev[10];
+ char rev[strlen(revision)+1];

if ((p = strchr(revision, ':'))) {
strcpy(rev, p + 1);

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